Beat the butter, granulated sugar, and brown sugar on medium speed (with a stand or hand mixer) until mixture is light and fluffy, about three to five minutes. Beat in the eggs and vanilla extract on medium speed until thoroughly combined, two to three minutes.

Mix together the flour, baking soda and salt. Add both chocolates to the flour mix and toss to combine. Turn the mixer to low speed (or continue to use a wooden spoon if mixing by hand) and slowly blend the flour-chocolate mixture into the butter-sugar mixture. Mix until the flour and chocolate are totally incorporated and the dough is completely mixed.

For best results, scrape dough into a container and let rest in the refrigerator for 3-4 hours before baking. Heat the oven to 350 degrees and position a rack in the centre of the oven. Drop the dough in heaping tablespoon balls onto a baking sheet about two inches apart. Press dough balls down slightly with the palm of your hand. Bake until cookies are golden brown on the edges and slightly soft in the center, about 12 minutes. Unbaked dough can be stored for up to a week in an airtight container in the fridge, or frozen in an air-tight container for 2-3 weeks.